Saturday, 21 December 2013

Trip report, 07/12/2013 Winter biodiversity in Smallcombe Cemetery

A hardy group of 15 people assembled on a dull damp day at
the entrance to the Cemetery to meet Alastair Cowan representing friends of St
Mary’s Cemeteries. Alastair explained
the plans for the Cemetery and his hopes that the biodiversity of the site
might be enhanced in the future. We
intended to assess what we could find in a morning and due to the season and
weather this was going to be limited.
Our task was made even harder by the Council having strimmed the site a
day or two before so that everything was covered with a layer of chopped grass.

Having established the need of the day Alastair guided us
around part of the Cemetery and we found much biographical detail (on the
gravestones) to interest us.

Despite the best efforts of the Council we were undeterred
in our plan to carry out a biodiversity assessment using bryophytes and snails
which was still possible if somewhat more difficult. I explained the technology of the biodiversity
assessment for bryophytes (using a dog lead and three canes) and we allocated
tasks. Alan and Marion Rayner were our
referees for identifying bryophytes. Andrew Daw set about exploring nooks and
crannies for snails, finding an impressive total of 16 species in all,
including blind, glass and grass snails.

I think most people expected to find very little, so it came
as rather a surprise that in the first circle we found 13 species. We continued
for another four circles and each circle took about 15 minutes to examine so
that after about an hour and a half we had examined 5 circles amounting to a
250 m2 area. Clearly this detailed examination of the gravestones
and grass is more fruitful of species than the traditional “surveying by
walking about”. By now everyone was getting a little chilled so we stopped
albeit that the method optimises at 20 circles.

The data were assembled and analysed using a method that I
have specially developed and applied widely to sites in the vicinity of Bath as
well as elsewhere in the UK.

We found a total of 24 species and the data indicated that
at least 30 would have been present. I
calculated a Nitrogen (pollution) index and the index was just over 5
indicating that the site is polluted (unpolluted would have an index of around
3). This therefore established a
baseline for us to check as progress is made in the restoration of the
site. Alan and Marion found a further
nine species either just outside our circles or on a previous visit so the
total of 33 for the site is an indication of the extent of suitable
surfaces/niches for bryophytes.

Pollution will presumably continue to be
a feature of the site and it was noticeable that the acidic granite and
sandstone gravestones had no bryophytes associated with them whilst the alkaline
limestone gravestones neutralized the acid and were “fertilized” by the
pollution.